1. Field of the Invention
The present invention relates to an apparatus for and method of driving a multi-nozzle piezo-inkjet head based on a digital grayscale.
2. Description of the Related Art
In general, a piezoelectric (PZT) actuator driving type inkjet head is configured to include a pressure chamber, a nozzle, a flow path, and a piezoelectric actuator that is an actuator for generating a driving pressure. To drive such a piezoelectric actuator, a driver for generating a driving voltage waveform is required.
For example, to briefly describe a process of ejecting droplets from a multi-nozzle piezo inkjet head, when a driver generates a voltage driving waveform and provides a piezoelectric actuator therewith, since the piezoelectric actuator is generally tightly adhered to a pressure chamber, a displacement of the piezoelectric actuator occurs according to the applied voltage driving waveform. The displacement generates pressure in the pressure chamber inside the inkjet head so that droplets inside the pressure chamber are ejected to the outside thereof through the nozzle.
Generally, in the case of a piezoelectric actuator driving type inkjet head, a voltage driving waveform in a range of 30 to 200 V is required, and the number of nozzles per inkjet head is approximately 10 to 1000. Various methods may be used to drive such a multi-nozzled inkjet head.
First, a method for driving a push-pull inkjet head according to the related art will be described. A high voltage driving waveform having the same form as a data signal is applied to the piezoelectric (PZT) actuator by using a push-pull amplification circuit.
In this regard, a magnitude of the voltage driving waveform applied to the piezoelectric actuator is the same as an operating voltage Vpp, and a form thereof is the same as that of a data signal. This method is very simple in the case of a multi-nozzle head, and thus a circuit unit of a head driving unit may be simplified.
However, a factor capable of changing the voltage driving waveform is restricted, to thereby allow a speed or volume of ejected droplets to be controlled through waveform duration only.
Meanwhile, in order to eject droplets of various sizes for implementing a grayscale, several waveforms having the same voltage level are implemented, and thus, droplets having different sizes may be ejected from an inkjet head.
However, it may not be easy to precisely adjust the speed of droplets having various sizes through the duration of a waveform having the same voltage level, and unstable droplets may be generated such that droplets may not be ejected any more.
As such, when droplets having various sizes have different speeds, locations at which droplets arrive on a printing media when being printed are different, problematically deteriorating printing quality.
The following Related Art Document relates to an apparatus for and method of driving an inkjet recording head and does not disclose a technology of driving a piezoelectric actuator inkjet head based on a digital grayscale.